Waterproofing mortar ammunition

ABSTRACT

Mortar ammunition comprising a bundle of superimposed sheets of gun-cotton is waterproofed by coating the edges of the bundle with a coating composition of nitrocellulose containing between 10.9 and 11.2 percent by weight nitrogen dissolved in a solvent which does not dissolve guncotton. On removal of the solvent a tough, tight-fitting film of said nitrocellulose is formed, which completely seals the edges of the bundle against water penetration between the sheets and is completely combustible, leaving no residue when the ammunition is fired. The coating composition has no adverse effect on ballistic properties.

United States Patent 1191 Axelrod 1 May 8, 1973 54] WATERPROOFING MORTAR 2,178,598 11 1939 McCormick ..102 49.2

AMMUNITION [75 lnventori Sydney Aztelrod, Nev/York N.Y. Pnmary Bummer-Robert F Stahl [22] Filed: Sept. 17, 1971 21 Appl. No.: 181,508 I [52] U.S. Cl. ..102/103, 102/492, 102/99 [51] Int. Cl. ..F42b l/00, F42b 13/22 [58] Field of Search ..l02/49.1, 49.2, 99, 102/100, 103

[56] References Cited UNITED STATES PATENTS 3,166,612 l/1965 Sauer et al ..149/12 2,918,005 12/1959 Schecter et al.. ..102/492 1,906,675 5/1933 Wagner ..102/104 3,304,867 Nadel ..102/D1G. 1

Assignee: The United States of America as represented by the Secretary of the Army Attorney-Edward .1 Kelly et al.

[57] ABSTRACT Mortar ammunition comprising a bundle of superimposed sheets of gun-cotton is waterproofed by coating the edges of the bundle with a coating composition of 4 Claims, 3 Drawing Figures 'PATENTEDRAY 81w V 3.731.634

FIG. 3

INVENTOR SYDNEY AXELROD 2 m w 4 w WATERPROOFING MORTAR THON The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to, me of anyroyalty thereon.

BACKGROUND OF THE INVENTION Sheet propellants for mortar ammunition are generally made from gun-cotton compounded with plasticizers, which may be energetic, e.g. nitroglycerine, or non-energetic, e.g. diethyl phthalate. Small amounts of other materials are also added to obtain certain physical characteristics. The composition is processed into sheets by standard methods. The sheets are stacked to; form a bundle, usually containing from two or ten sheets, which is then sewn along either two adjoining or two opposite sides to hold the sheets together (one sheet is considered as one-half increment, two sheets as one increment). Only two sides are sewn so as to permit ready removal of one or more sheets from the bundle, if required, to adjust the amount of propellant to the desired range for the projectile. Because of the physical structure of the sheet ammunition thus obtained, water can penetrate and become trapped between the sheets and cause serious degradation of the burning of the propellant when the ammunition is fired. Such degradation of propellant combustion results in short rounds (rounds which fall short of the intended range), which constitute a serious safety hazard and may cause casualties among our soldiers.

Numerous attempts have been made to solve the problem of waterproofing, i.e., protecting the ammunition from becoming wet, as is frequently encountered in field use. These attempts have included the use of plastic films, e.g., of cellophane and polyethylene, to completely surround the sheet propellant bundle or increment. The plastic film wrapping must be sealed by means of heat or a solvent, which is a time-consuming and costly process. These films are often not completely consumed during the ballistic cycle and leave objectionable residue on the walls of the mortar tube. This residue causes a slow descent or a hang-up when the succeeding round is dropped into the mortar tube. Such interference with the firing sequence is a hazardous condition which must be eliminated. In addition, a damaged plastic film wrapping on the sheet propellant allows water to penetrate between the sheets and result in a lower ballistic level, which may cause short rounds. Further, the propellant is subjected to physical stress during handling, loading, shipping and finally when used in the field by the troops, during which the comers of the sheets or bundle will frequently break off. This results in a reduced propellant charge, which also results in short rounds.

No satisfactory solution to the aforesaid problem relative to sheet propellants for mortar ammunition has been found to date.

It is an object of this invention to provide a novel method for water-proofing sheet propellants which prevents penetration of water, oil, dirt, etc. between the sheets and at the same time protects the sheets against physical damage.

Another object of the invention is to provide sheet propellant increments or bundles, with a novel waterproofing coating, which leaves no residue in the mortar tube and protects the propellant against short rounds resulting from the presence of water or breakage of corners of the sheets.

Other objects will be obvious or appear from the description of the invention set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a mortar sheet propellant bundle of the invention prior to application of waterproof coating.

FIG. 2 is a perspective view of the mortar sheet propellant bundle shown in FIG. 1 after application of the waterproof coating.

FIG. 3 is a vertical cross section of the coated bundle taken through the plane A, A of FIG. 2.

DESCRIPTION OF THE INVENTION According to this invention, mortar propellant sheet increments or bundles consisting essentially of guncotton, which term for purposes of this invention denotes nitrocellulose containing at least 12.6 percent by weight of nitrogen, are coated on their edges with a solution of nitrocellulose containing between about 10.9 and 11.2 percent nitrogen in an organic solvent, which does not dissolve the guncotton. When the coating composition thus applied is allowed to dry, a strong, tough, homogeneous, water repellent film is formed. This film completely coats and seals the edges of the propellant bundle, thereby preventing water from entering between the sheets. At the same time this tight fitting film mechanically holds the edges of the sheets together and protects the corners of the sheets against breakage. Another important advantage of the invention is that any penetration of the coating composition between the propellant sheets will not cause the sheets to adhere to each other. Further, since the solvents in the coating composition are not solvents for guncotton, they do not exert a harmful solvating action on the propellant which would cause the sheets to adhere to each other. Sheets in the increment or bundle should not adhere to each other, since it will affect the burning and thus the ballistics of the round when it is fired. The sheets should additionally not adhere to one another, since under certain firing conditions, it is sometimes necessary to be able to readily remove one or more sheets without tearing or damaging the remaining sheets in order to change the ballistic level of the round.

Suitable organic solvents for preparing the coating compositions, which are capable of dissolving nitrocellulose of 10.9 to 11.2 percent nitrogen content but incapable of solvating guncotton, include anhydrous ethanol, ethanol containing up to about 10 percent water, and mixtures thereof with toluene containing up to about one-third part by weight toluene per part of ethanol. The concentration of the nitrocellulose in the coating composition may vary from 10 to 50 percent by weight, depending on the method of application. The coating compositions may contain up to about 20 percent by weight of plasticizers compatible with said nitrocellulose, e.g., nitroglycerine, triethyleneglycol dinitrate, dibutyl phthalate, dioctyl adipate, ethyl cellulose, hydroabietyl alcohol and blown soybean oil.

The coating compositions can be applied in any suitable manner to the edges of the propellant sheet increment or bundle, e.g., brushing, spraying or dipping. The coating operation is not critical, since the solvents in the coating composition do not affect the propellant sheets. The outer sheets of the bundle may also be partially or completely coated during the coating operation; however, since the propellant sheets per se are essentially water repellent, for the purpose of waterproofing the bundle it is necessary only to coat the edges of the bundle so as to prevent penetration of water between the sheets. The thickness and amount of coating deposited on the edges of the sheet propellant bundle may vary widely, since the nitrocellulose of about 10.9 to 1 1.2 percent nitrogen content is completely combustible and leaves no residue when the propellant is fired.

The nitrocellulose used in the coatings of this invention contains between about 10.9 and 11.2 percent nitrogen. This is important, since nitrocellulose of substantially lower nitrogen content is less completely combustible and will produce undesirable residue on firing of the mortar increments, while the use of nitrocellulose of substantially greater nitrogen content requires the use of solvents having a harmful solvating action on the propellant sheets, as noted above.

The following examples illustrate the invention:

EXAMPLE 1 The mortar sheet propellant employed in this example consisted of a bundle of 10 superimposed sheets, each approximately 2% inches square, 0.023 inch thick and weighing 50 grains, having the following composition by weight:

Nitrocellulose (13.25% Nitrogen content) 52.15% Nitroglycerine 43.00% Potassium Nitrate 1.25% Diethyl Phthalate 3.00% Ethyl Centralite (N,N'-diethyl carbanilide) 0.60%

As shown in FIG. 1, this sheet bundle 1 was sewn along two opposite sides 2 and 3 with silk thread in usual manner, to hold the sheets 4 together. As usual, only two sides were sewn in order to facilitate removal of a sheet from the bundle, if desired, to adjust the amount of propellant to provide the desired range for the projectile. The sheets and bundle possessed a center hole 5 of about 1% inches diameter and a cut 6 extending from said hole to the edge of the bundle, whereby the flexible bundle could be opened at out 6 to permit insertion of the boom (ignition cartridge housing) ofa mortar into hole 5.

A coating composition of the following formulation (parts by weight):

One-fourth Sec. Nitrocellulose (10.9 l 1.2%

Nitrogen) 25 parts Dibutyl Phthalate 5 Toluene 24 Ethanol (92.5%) 76 was prepared by stirring the nitrocellulose gradually into a previously prepared mixture of the other components until the nitrocellulose was completely dissolved.

The coating composition, was brushed onto all edges of the bundle, including the center hole 5 and cut 6, the bundle being sufficiently flexible to permit pressing the brush through said out to coat the edges thereof, after which the coatings were allowed to dry by evaporation of the solvent. As shown in FIGS. 2 and 3, the coating thus obtained formed a tight fitting, tough film 7 which mechanically held all edges of the sheets together and completely sealed all edges of the sheet bundle against penetration of water. By sharply twisting or bending the bundle, the film was readily broken to permit removal of one or more sheets. Examination revealed that the individual sheets had not been adhered to each other, showing that the solvent had not attacked the sheets and that the coating composition had not cemented the sheets together where it had penetrated between the sheets.

Several bundles of sheet propellant coated in the aforesaid manner were assembled as part of the mortar propelling charge and the assembled ammunition was fired in a mortar. No residue was found in the mortar tube after the firing.

ln the foregoing example, the dry weight of the coating was 0.20 gram and the weight of the sheet bundle before coating was 32.4 grams.

Several bundles identical with the one described above were brush-coated on their edges in the foregoing manner, the number of applications being varied to provide coatings of different thicknesses. The heaviest coating thus obtained weighed 0.65 gram, and thus was more than three times as thick as the one shown in the example. All of the coated bundles thus obtained, when fired under the same conditions as above, left no residue in the mortar tube and exhibited normal, satisfactory ballistic properties.

By way of comparison mortar sheet propellant bundles described in Example 1 were coated in the foregoing manner with a lacquer consisting of a solution of guncotton (nitrocellulose of 12.6 percent nitrogen content) in a conventional solvent consisting of about percent acetone and 25 percent toluene. This solvent, unlike the solvent used in the example, attacked and dissolved the propellant sheets. Examination revealed that the sheets had become cemented together where the solvent had penetrated between the sheets. This condition resulted in poor ignition, incomplete burning and poor ballistic range when the propellant was fired in a mortar.

EXAMPLE 2 The process of Example 1 was repeated with similar results by employing a coating composition of the following formulation:

One-half Sec. Nitrocellulom (10.9 l 1.2%

Nitrogen) 15 parts Diethyleneglycol Dinitrate 2 Toluene 25 Butanol (99%) 7.5 Ethanol (925%) 67.5

EXAMPLE 3 The process of Example 1 was repeated with similar results by employing the following coating composition:

One-fourth Sec. Nitrocellulose (10.9 1 1.2%

Nitrogen) 20 parts Nitroglycerine 4 Ethanol, Anhydrous 100 It is evident from the foregoing that the invention provides an important technical advance in the art of waterproofing mortar sheet propellant increments in that it produces products, which are not only effectively protected against water, but leave no dangerous residue when fired and possess reliable ballistic properties. The prior art methods and products have not provided such protection and performance. This invention is surprisingly simple, inexpensive and effective and constitutes a major step forward.

I wish it to be understood that I do not desire to be limited to the exact detail of construction shown and described for obvious modification will occur to a person skilled in the art.

What is claimed is:

l. A process for waterproofing mortar ammunition comprising a bundle of separate, superimposed sheets consisting essentially of nitrocellulose of at least 12.6 percent nitrogen content, which comprises coating the edges of said bundle with a coating composition consisting essentially of nitrocellulose of between about 10.9 and l 1.2 percent nitrogen content dissolved in an organic solvent which does not dissolve said nitrocellulose of at least 12.6 percent nitrogen content, and thereafter removing the solvent, thereby forming a tough, tight-fitting film of said nitrocellulose of between about 10.9 and 1 1.2 percent nitrogen content, which completely seals the edges of the bundle against water penetration between said sheets without causing the sheets to adhere to each other, said film leaving no residue when the propellant is fired and having essentially no effect on the ballistic properties of the propellant.

2. A process as set forth in claim 1, wherein the solvent is selected from the group consisting of anhydrous ethanol, ethanol containing up to about 10 percent water, and mixtures thereof with toluene containing up to about one-third part of toluene per part of ethanol.

3. A process as set forth in claim 2, wherein the coating composition contains 10 to 50 percent by weight of said nitrocellulose and 0 to 20 percent by weight of a plasticizer based on the weight of said dissolved nitrocellulose.

4. A process as set forth in claim 3, wherein the coating composition consists essentially of the following components:

Nitrocellulose (10.9-l 1.2%N) 15-25 parts Ethanol (92.5%) Toluene 25 lasticizer of the group consisting of Dibutyl Phthalate, Nitroglycerine and Diethyleneglycol Dinitrate 2-5 

2. A process as set forth in claim 1, wherein the solvent is selected from the group consisting of anhydrous ethanol, ethanol containing up to about 10 percent water, and mixtures thereof with toluene containing up to about one-third part of toluene per part of ethanol.
 3. A process as set forth in claim 2, wherein the coating composition containS 10 to 50 percent by weight of said nitrocellulose and 0 to 20 percent by weight of a plasticizer based on the weight of said dissolved nitrocellulose.
 4. A process as set forth in claim 3, wherein the coating composition consists essentially of the following components: Nitrocellulose (10.9-11.2%N) 15-25 parts Ethanol (92.5%) 75 ''''Toluene 25 ''''Plasticizer of the group consisting of Dibutyl Phthalate, Nitroglycerine and Diethyleneglycol Dinitrate 2-5 '''' 